It is important that hair spray compositions have good holding ability for the curl without giving a harsh, brittle feeling to the hair. Furthermore, the hair spray should be water soluble so that it can be washed out of the hair at the time it is shampooed.
The most commonly employed polymer ingredient of hair sprays is a copolymer of methyl vinyl ether with maleic acid or maleic anhydride. These polymers are not water soluble.
Since water solubility is a desired feature of hair sprays, the resin is partially neutralized by reacting the free carboxylic groups of the polymer with a base, such as ammonia, dimethylamine, diethylamine, diethanolamine, triethanolamine, triisopropanolamine, 2-methyl-2-amino-1-propanol, and the like. Most commercial hair sprays, whether dispensed from pressurized aerosol containers or from manual pump dispensers, are of the aforementioned type. Typical compositions of this type are described, for example, in U.S. Pat. Nos. 3,922,341 and 4,164,562.
Whereas, the alcoholic solutions of the copolymer are considered stable and have relatively good shelf life, the solutions of the partially neutralized copolymer tend to darken upon standing at room temperature within a few months and much faster at elevated temperatures. The rate of the discoloration of the initially clear solution of the partially neutralized resin, and the intensity of the discoloration depends on the particular base that is employed for neutralization. Although the discoloration can be substantially reduced by the use of different neutralizing bases, the requirement of good curl-holding ability of the ultimate product often compels the use of certain neutralizing base compounds which result in a more pronounced darkening effect than can be obtained with some other bases.
A number of other polymers were neutralized with aminomethylpropanol, including an octylacrylamide/acrylates/butylaminoethyl/methacrylate copolymer (this is a CTFA name, according to the CTFA Cosmetic Ingredient Dictionary 1977) and sold under the name Amphomer by the National Starch Co.; polyvinylpyrrilydone; and a polyvinylpyrrilydone/polyvinylacetate copolymer. None of these resins presented any discoloration problem either in their original form, or in an alcoholic solution; or in their partially neutralized form. Therefore, it appears that the special discoloration problem which we found is peculiar only to solutions of the specific partially neutralized vinyl ether/maleic acid copolymers which are most frequently used in hair sprays.
In view of the unappealing discoloration of hair sprays, products of this type have been heretofore sold in opaque aerosol or manual pump dispensing containers. It has become desireable, however, for marketing reasons, to eliminate the darkening of the neutralized resin solutions upon standing so that a commercially useful hair spray product can be obtained which can be packaged and sold in clear bottles without the development of unappealing discoloration.